As is known, electronic noses are instruments which allow continuously analysing the ambient air. Electronic noses are capable of classifying the quality of a gas coming from an environment to assign a specific olfactory class or to olfactarily quantify the gas analysed, by assigning an olfactory class to the gas and estimating its odour concentration.
The operation of the electronic nose follows that of the human olfactory system and is generally divided into steps:                measuring the gas using suitable sensors;        processing the signals coming from the sensors;        recognising the odours;        
The electronic noses comprise an intake duct, which connects the outside environment with a measuring chamber. The circulation of the gas through the electronic nose is usually guaranteed by a suction device. The suction device may be, for example, a pump or a fan.
The measuring chamber, which is usually made of a chemically inert material, houses a matrix of sensors. The calibration of the sensors of the electronic nose is performed using the passage of a reference gas (usually air) inside the measuring chamber, in such a way as to establish a baseline for the response of the sensors.
Electronic noses, like other measuring apparatuses, for example gas chromatograph equipment, require a source of clean air, that is odourless air, such as zero air; the clean air may serve for example to generate a reference odour by mixing the clean air together with molecules of butanol, or to regulate a humidity level of the air inside the measuring apparatus.
Often, in measuring apparatuses requiring clean air, the latter is supplied by a cylinder integrated in the apparatus.
However, this solution has the drawback of increasing the size and cost of the apparatus. Moreover, the use of a cylinder has problems linked to maintenance and replacement, thus not providing the best practical and safety conditions.
Alternatively, measuring apparatuses requiring clean air have a device on board for generating the air clean.
In order to generate clean air, in the context of small devices that can be used on board a measuring apparatus (such as for example an electronic nose), the prior art teaches the use of catalytic oxidisers.
These catalytic oxidisers normally use the oxides of precious metals (for example platinum or palladium) as catalysers and comprise a furnace for heating the infeed air.
However, this solution also has drawbacks, mainly associated with the fact that it requires increased energy, with consequent increases in the management costs.
Examples of devices to generate clean air can be found in the following patent documents: DE3929521A1, EP0398766A1, WO2009/068965A1, U.S. Pat. No. 5,134,080A, EP0317299A2, US20121279227. However, these documents do not provide effective solutions applied particularly to measurement apparatuses, such as in particular electronic noses.